The invention relates generally to disc drives and specifically to reducing the acoustic noise generated when a disc drive undergoes a seek operation.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are typically coated with a magnetizable medium and mounted on the hub of a spin motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by transducers (xe2x80x9cheadsxe2x80x9d) mounted to an actuator assembly for movement of the heads relative to the discs. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
The heads are each mounted via flexures at the ends of actuator arms that project radially outward from the actuator body or xe2x80x9cExe2x80x9d block. The actuator body typically pivots about a shaft mounted to the disc drive housing adjacent the outer extreme of the discs. The pivot shaft is parallel to the axis of rotation of the spin motor and the discs, so that the heads move in a plane parallel to the surfaces of the discs.
Typically, such actuator assemblies employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor typically includes a flat coil mounted horizontally on the side of the actuator body opposite the actuator arms. The coil is immersed in a vertical magnetic field of a magnetic circuit comprising one or more permanent magnets and vertically spaced apart magnetically permeable pole pieces. When a controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the head to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
The movement of the actuator so that the head moves from one position to another is called a xe2x80x9cseek.xe2x80x9d Typically, a seek is controlled by a feed forward/feedback actuator servo control system. The DC current generated by the control system is derived from a velocity profile which governs how the actuator is accelerated from its initial position, the maximum velocity the actuator achieves and how the actuator is decelerated to complete its movement at the final position of the seek. Thus the attributes of the velocity profile determine the overall seek time. Typically, the acceleration rate, maximum velocity and deceleration rate in the velocity profile are the maximum allowable by the hardware in order to minimize the seek time. In a typical disc drive, there is only one velocity profile that governs actuator movement, regardless of whether the drive is idle, seeking in response to a user command or seeking in response to a command from some other source such as a network.
Disc drive seek operations create audible noise. The noise created is related to a number of factors including the overall seek speed, the specific attributes of the velocity profile and the disc rotating speed. Disc drive users recently have required higher data storage capacities and increased performance in drive designs resulting in faster seek times, faster disc rotation speeds, higher actuator assembly velocities and higher rates of acceleration and deceleration; all of which increase the audible noise from the drive.
The increased noise from disc drives has become a perceived problem in today""s office environment by many users. Normally, the sound of a seeking disc drive is comforting to users when they have issued a save command or when they know the drive should be seeking. However, most disc drives today also perform seeks which are not initiated by the user during idle periods and when given network commands. Typical disc drives automatically perform self-diagnostic and maintenance seeks during idle periods and also seek to random positions to prevent the furrowing or migration of lubricant on the surfaces of the discs. The noise generated by seeks not initiated by a command from the user can be annoying to the user because most users do not understand why the drive is seeking. In fact, noise from idle period seeking and seeking due to commands unknown to the user have caused some users to believe that their drive is broken or malfunctioning.
Against this backdrop the present invention has been developed. It has been determined that audible seek noise can be reduced by slowing the seeking of the actuator arm, although during drive operation this not desirable because the users demand fast response to their commands. However, during periods when the drive is idle and awaiting commands from the user, minimizing the seek times is not a priority. Generally, most commands not initiated by the user do not require minimizing seek times. Also, it has been further determined that different actuator positions relative to the discs cause differing amounts of audible noise. In some cases the audible noise can vary up to 1 decibel (dB) between different actuator positions on the discs, which corresponds to a factor of 10 difference in the acoustic power generated depending on the actuator position. This noise is additional to the audible noise generated by the seeking of the actuator discussed above.
The method and apparatus in accordance with the present invention utilizes the two observations mentioned above to minimize audible noise generated by idle disc drives due to the seeking and position of the actuator. The method and apparatus also includes minimizing the audible noise for any seeking not initiated by the user.
Accordingly, an aspect of the invention is found in a method of minimizing audible seek noise in drive for any seeking not initiated by the user. This method includes a step of developing a low-noise velocity profile specifically designed to reduce the noise generated by movement of the actuator during seeking. This profile adjusts the acceleration, maximum velocity and deceleration to minimize the noise produced from the act of moving the actuator. Next, the low-noise velocity profile is selected during idle periods to govern all movement of the actuator. In addition, use of the low-noise velocity profile can be extended to all movement of the actuator not initiated by the user.
Another aspect of the invention is found in a method of minimizing audible noise in an idle disc drive using the observation that different actuator positions are relatively noisier than others. The method includes a step of rotating the actuator assembly to a plurality of actuator assembly positions. The actuator positions may correspond to tracks on the disc but this is not required. Next, a noise level associated with each actuator assembly position is determined and this information is used to adjust the drive operation during idle periods to minimize audible noise from the drive. In the present invention, the information is used in controlling actuator seeking and position selection during idle periods.
In one aspect of the invention, the noise level information is used during idle period seeking to adjust the velocity profile of the seek to minimize the overall noise generated by the seek. This is done by including the position noise as a part of a function that describes the overall noise created by seeking from one position to another and includes the noise generated by the act of accelerating, moving and decelerating the actuator based on the velocity profile.
Solving the function for a minimum produces a velocity profile that minimizes the overall noise generated during the seek.
In another aspect of the invention, the noise level of each position is used to determine what actuator positions are used and how long the actuator spends in each position during idle periods. One alternate method includes determining a set of actuator positions that are the least noisy, and using only positions from that set during idle periods, selecting from that set randomly or by some other method. The preferred method includes randomly selecting actuator positions during idle periods from the range of all possible positions, and adjusting the duration that the actuator is placed in the selected position based on the determined noise level of that position such that the amount of time the actuator arm assembly spends in the relatively noisier actuator positions is reduced.
These and other features as well as advantages that characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.